Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare this is a safe, idempotent, closed-world read/compute operation, so the safety burden is lifted. The description earns credit by disclosing the underlying model that shapes the answer: bulk constant-current phase to ~80% SoC, then tapering absorption phase to 100%, applicable to solar, shore power, or alternator. That context matters for interpreting the result, though it doesn't mention assumptions about efficiency losses or whether the estimate is an upper/lower bound.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Three short sentences: the purpose comes first, then the modeling assumptions that qualify the answer, then applicable charging sources. No filler, though the final sentence is closer to nice-to-have than essential.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description should convey enough to anticipate the return, and the two-phase discussion does that for a simple numeric estimate. Minor gaps: it doesn't state the unit of the returned duration or note that absorption time is an approximation, which would help an agent present the result.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so every parameter is already documented in the schema. The description adds no syntax, unit, or edge-case guidance beyond what the schema provides (e.g., no note on how chargeCurrentAmps overrides the power-derived current). Baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Estimate how long it takes to charge a battery bank') plus the scope (from a given SoC to a target level). It is clearly distinguishable from siblings like calculate_battery_bank or calculate_power_budget by resource, though it never explicitly contrasts itself with them.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage is implied by the description — use this when you need a charge-duration estimate for a battery bank. There is no explicit when-not-to-use condition and no alternative tool is named, so the agent must infer boundaries from the sibling list.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.